The invention set forth in this specification pertains to the control of the speed at which a rotor in a generator such as an alternator is operated when the generator is driven by a source of mechanical power such as a spring motor which delivers or is capable of delivering a variable amount of mechanical power to the generator.
The invention is intended to be utilized in connection with small, spring motor powered, portable cassette tape players. To be acceptable from a cost standpoint such devices must be comparatively inexpensive, comparatively simple in construction, and comparatively reliable in operation. Further, to achieve these characteristics such devices must be constructed in such a manner as to minimize the number of parts employed in them. In order for such a tape player to operate it is necessary to utilize within it a generator such as an alternator to provide electrical power to operate an amplifier. The rotation of the rotor of the generator in this type of device should be held relatively constant in order to minimize the problems in connection with the construction of the amplifier. Also it is necessary in such a device to provide a mechanical output in the form of rotation at a constant speed in order to satisfactorily drive the tape mechanism employed.
It is well known that a spring motor is normally constructed so that its mechanical output will vary in accordance with the mechanical energy stored with a spring and that the amount of such energy will decrease as the spring motor is operated. As a consequence of this a spring motor will normally deliver a variable mechanical output to a generator in a tape player type device as indicated in the preceding discussion unless means are employed to regulate or govern the output of the spring motor. Further, such spring motors will not provide uniform mechanical outputs for driving the tape mechanisms unless such regulation or governing means are provided. A number of different devices and structures have been proposed for this purpose.
Most commonly, mechanical governors have been proposed for use with spring motors since such mechanical governors are available as a result of extensive work which has been done in connection with the utilization of spring motors in all sorts of applications. It has also been proposed to regulate the speed at which a generator is operated by a spring motor through the utilization of a solenoid type latch device which operates in accordance with the voltage produced by a governor. It has also been proposed to govern generator speed in the combination of a spring motor and a generator by varying the load on the generator. In one application of this type of control a diode has been utilized which becomes conductive at a predetermined voltage so as to increase the load on the generator at such voltage.
It is not considered that any of such procedures are particularly desirable. Mechanical governors have the familiar problems inherent with moderately complex mechanical devices. The use of a latch type device as indicated in the preceding to a degree also has the problems associated with the use of any other essentially mechanical device. Various previously known electrical expedients involving changing the load on the generator are not considered to be effective in achieving the precise degree of control necessary so that the controlled speed of the generator can be utilized for the mechanical purpose of operating a tape playback mechanism at a uniform speed. In an application such as the intended application of the invention reasonably accurate speed control is necessary if the sound playback mechanism is to operate satisfactorily.